Structural implications of AB2s. Are novel D segments involved with anti-idiotypic specificity?

For these studies it is clear that within an antigenic system, syngeneic anti-idiotypic antibodies are restricted in their use of germline gene segments. They differ considerably from either allogeneic Ab2s recognizing public idiotopes or syngeneic Ab2s recognizing private idiotopes which are structurally heterogeneous. The D segments of Ab2s in a variety of systems are novel in structure and cannot easily be explained by previously described germline D segments. D-D fusion contributes to the generation of the third hypervariable region in these antibodies. It is not completely clear whether or not this mechanism plays a more important role in generating Ab2s than it does in generating other antibodies. Finally, somatic mutation does occur in anti-idiotypic antibodies. It is unlikely that the idiotypic network, per se, is strictly germline encoded. On the contrary, somatic events (i.e. mutation, junctional diversity, etc.) are probably important in the generation of anti-idiotypic antibodies.